You have got to give the WordPress Community some serious props for being on top of these types of issues and especially over the holidays.
Version 3.0.4 of WordPress, available immediately through the update page in your dashboard or for download here, is a very important update to apply to your sites as soon as possible because it fixes a core security bug in our HTML sanitation library, called KSES. I would rate this release as “critical.”
This is the third update released in the last 30 days to address security issues so if for some reason you have not applied the 3.0.2 and 3.0.3 updates you should do that now along with this update.
I just did the update on my sites and it was very quick and painless thanks to the Automatic Update process.